¾ cup plus 2 tablespoons cake flour
¾ cup plus 1 tablespoon all-purpose flour
¼ cup granulated sugar
2 teaspoons kosher salt
4 large eggs
5 large egg yolks
1 stick (8 tablespoons) unsalted butter, melted and cooled slightly
2 cups whole milk
3 tablespoons Armagnac or cognac
1¼ cups confectioners' sugar
4 cups mascarpone cheese
½ cup sweet Marsala wine (or half as much rum or coffee liqueur)
¼ cup natural cocoa powder
1. Make the crepe batter: In a fine-mesh sieve set over a medium bowl, sift together the cake flour, all-purpose flour and sugar. Whisk in the salt. In another medium bowl, whisk together the eggs and egg yolks. Add the egg mixture to the flour mixture and whisk until smooth and webby (it will be very thick). In a slow, steady stream, whisk in the butter, then the milk and the Armagnac, until the batter is smooth (if there are any lumps, strain the batter through a fine-mesh sieve and into a medium bowl). Cover the bowl with plastic wrap and refrigerate for 1 hour.
2. Line a baking sheet with parchment paper. Set an 8-inch nonstick skillet over medium-high heat. Gently stir the crêpe batter, then pour ¼ cup of batter into the skillet. Holding the skillet by the handle, tilt and turn the skillet to quickly disperse the batter. Cook the crepe until the underside is golden-brown, about 1½ minutes. Lightly jerk the skillet to loosen the crepe, then flip the crepe over using a spatula, a more vigorous jerking motion or your fingers. Cook on the other side until golden-brown, about 30 seconds, then slide the crepe onto the parchment-paper-lined baking sheet. Repeat until all of the batter is used (you'll end up with about 20 crepes total, and will need 18 for the cake). Refrigerate the crepes on the baking sheet until completely chilled, at least 2 hours or overnight.
3. Make the tiramisu filling: In a fine-mesh sieve set over the bowl of a stand mixer, sift the confectioners' sugar. Add the mascarpone cheese and the Marsala wine. Use the paddle attachment to combine the mixture on low speed until well combined.
4. Remove the crepes from the refrigerator. Add 1 crepe to the bottom of an 8-inch springform pan so it lies flat. Add ¼ cup of the tiramisu filling to the center of the crepe and use a small offset spatula to evenly spread the filling over the crêpe. Repeat with the filling and 17 more crêpes. Refrigerate the leftover filling; you'll use it to finish the cake. Chill the cake in the refrigerator for at least 2 hours or overnight.
5. Remove the cake from the refrigerator, undo the springform pan and set set it on a cake plate or platter. Spread the remaining tiramisu cream on top of the cake. Add the cocoa powder to a fine-mesh sieve and sprinkle it over the top of the cake. Slice and serve.